Properties of polyamide 612/poly(vinyl alcohol) blends and their impact on free volume and oxygen barrier properties

Oxygen transmission rates and free volume properties (i.e. average volumes of free-volume-cavities (V_f), mean number of the free volume cavities per unit volume (I₃) and fractional free volume (F_v)) values of bio-based polyamide 612 (PA612)/poly(vinyl alcohol) (PVA) (i.e. PA612_xPVA⁰³ _y, PA612_xPVA⁰⁵ _y, PA612_xPVA⁰⁸ _y and PA612_xPVA¹⁴ _y) blend films were reduced to a minimum value, when their PVA content reached corresponding optimal values of 25, 20, 15 and 10 wt%, respectively. The minimum oxygen transmission rate, V_f, I₃ and F_v value obtained for the best PA612₉₀PVA¹⁴ ₁₀, PA612₈₅PVA⁰⁸ ₁₅, PA612₈₀PVA⁰⁵ ₂₀ and PA612₇₅PVA⁰³ ₂₅ bio-based blown films reduced considerably with decreasing PVA degrees of polymerization. As evidenced by the results of dynamical mechanical analysis, differential scanning calorimetry, wide angle X-ray diffraction and Fourier transform infrared spectroscopic experiments, PA612 and PVA are miscible to some extent at the molecular level when their PVA contents are ≤ the corresponding optimal values. The significantly improved oxygen barrier and free volume properties for the PA612_xPVA^z _y blend films with optimized compositions is at least in part to the enhanced intermolecular interactions between PA612 carbonyl groups and PVA hydroxyl groups.